tachycardia (means fast heart rate) syndrome
Yes, simple yoga won't produce a lot of sweat, but some asanas can, so start off with beginner yoga and don't push yourself too hard. Stay away from Hot Yoga if you don't want to sweat.
Isometrics shouldn't cause you to sweat as long as you don't push it to the point that you create excessive resistance. Some isometric exercises might require position changes, but so does everyday living. If you are able and your health insurance covers it, I suggest asking your doctor to refer you to Physical Therapy or Occupational Therapy to help develop the best exercise program for you. There is a physician in Dallas who has developed a protocol that your doc may have already mentioned. If not, you may find this interesting:
https://www.medbridgeeducation.com/...uation-treatment-and-the-covid-19-connection/
And here is another good resource:
Dysautonomia International: Exercises for Dysautonomia Patients
Low impact walking is a good one, as well. I know it's hard to walk outdoors in Texas this time of year without sweating, so if you can find an indoor place to walk, like an indoor Mall, that would be best. Remember the Mall Walking trend that started up back in the 60's I think it was? The CDC even has a '
Mall Walking Program Resource Guide' with annotated research.
Another low-impact and low sweat exercise is pool exercise, which even if you sweat, being in a pool can help alleviate that issue. If available near you, maybe you can join organized pool exercise classes. Maybe at the YWCA or a community pool. Some insurance companies even provide support or discounts for joining gyms. So I'd suggest looking into that, too. Sometimes just paying the fee for the class without joining the gym is a possibility, but that depends on the programs available near you. Our community center has programs like that where a paid membership is not required, but I know not everyone has things like that within a reasonable distance.
Just a few thoughts and references for you. I hope they help and I really encourage you to do get in touch with one of the support groups for POTS. Here are some links to help you find one that might appeal:
http://www.dysautonomiainternational.org/page.php?ID=24https://www.spoonsandbrainfog.com/home/support-groupshttps://www.rarediseasesnetwork.org/cms/autonomic/Get-Involved/Patient-Advocacy